The present application generally relates to permanent magnet DC motors (PMDC motors), and specifically to facilitating feedforward torque and current control of such motors.
Permanent Magnet DC (PMDC) motors are widely employed for motion control applications such as in electric power steering (EPS) systems, power tools, among others. The torque control of PMDC motor drives is performed through current regulation utilizing measured current feedback (through current measurement circuitry). Feedback current control performed in such a manner provides tunable current (and thus torque) control bandwidth characteristics, improved disturbance rejection and reduced sensitivity to modeling uncertainty. Another advantage of using PMDC motor drives with feedback control operation is that position or velocity measurements are not required for control. It should be noted however that motor velocity is an important signal that enhances system control performance as it can be used for power limiting, compensator gain scheduling and other similar control features.
Feedforward current and torque control of PMDC motor drives is another mode of operation. Feedforward control mode requires an accurate model of the machine, including nonlinearities (such as brush drop voltage), and has low bandwidth (limited by sampling rate) and poor disturbance rejection performance characteristics. However, it is typically not prone to instabilities (due to open loop nature) and is noise free because current sensors are not usually required for implementation of feedforward control. Further, the noise transmission characteristics of feedforward control systems is lower as compared to feedback control systems.
Accordingly, it is desirable to use feedforward current control to operate PMDC motors in applications, such as EPS systems, power tools, among others.